• First Lapita Settlement and its Chronology in Vava'u, Kingdom of Tonga

      Burley, David V.; Connaughton, Sean P. (Department of Geosciences, The University of Arizona, 2007-01-01)
      Beginning approximately cal 1400 BC, Austronesian-speaking Lapita peoples began a colonizing migration across Oceania from the Bismarck Archipelago to western Polynesia. The first point of entry into Polynesia occurred on the island of Tongatapu in Tonga with subsequent spread northward to Samoa along a natural sailing corridor. Radiocarbon measurements from recent excavations at 4 sites in the northern Vavau islands of Tonga provide a chronology for the final stage of this diaspora. These dates indicate that the northern expansion was almost immediate, that a paucity of Lapita sites to the north cannot be explained as a result of lag time in the settlement process, and that decorated Lapita ceramics disappeared rapidly after first landfalls.
    • The Marine ΔR for Nenumbo (Solomon Islands): A Case Study in Calculating Reservoir Offsets from Paired Sample Data

      Jones, Martin; Petchey, Fiona; Green, Roger; Sheppard, Peter; Phelan, Matthew (Department of Geosciences, The University of Arizona, 2007-01-01)
      It is necessary to calculate location-specific marine Delta-R values in order to calibrate marine samples using calibration curves such as those provided through the IntCal98 (Stuiver et al. 1998) data. Where known-age samples are available, this calculation is straightforward (i.e. Stuiver et al. 1986). In the case that a paired marine/terrestrial sample calculation is performed, however, the standard calculation (i.e. Stuiver and Braziunas 1993) requires that the samples are treated as relating to isochronous events. This may not be an appropriate assumption for many archaeological paired samples. In this paper, we present an approach to calculating marine Delta-R values that does not require the dated events to be treated as isochronous. When archaeological evidence allows the dated events to be tightly temporally constrained, the approach presented here and that described by Stuiver and Braziunas (1993) give very similar results. However, where tight temporal constraints are less certain, the 2 approaches can give rise to differing results. The example analysis considered here shows that a Delta-R of 81 +/- 64 14C yr is appropriate for samples in the vicinity of Nenumbo (Reef Islands, southeast Solomon Islands) around the period 2000-3000 BP.
    • Mortar Dating Using AMS 14C and Sequential Dissolution: Examples from Medieval, Non-Hydraulic Lime Mortars from the land Islands, SW Finland

      Lindroos, Alf; Heinemeier, Jan; Ringbom, Åsa; Braskén, Mats; Sveinbjörnsdóttir, Árny (Department of Geosciences, The University of Arizona, 2007-01-01)
      Non-hydraulic mortars contain datable binder carbonate with a direct relation to the time when it was used in a building, but they also contain contaminants that disturb radiocarbon dating attempts. The most relevant contaminants either have a geological provenance and age or they can be related to delayed carbonate formation or devitrification and recrystallization of the mortar. We studied the mortars using cathodoluminescence (CL), mass spectrometry (MS), and accelerator mass spectrometry (AMS) in order to identify, characterize, and date different generations of carbonates. The parametersdissolution rate, 13C/12C and 18O/16O ratios, and 14C age were measured or calculated from experiments where the mortars were dissolved in phosphoric acid and each successive CO2 increment was collected, analyzed, and dated. Consequently, mortar dating comprises a CL characterization of the sample and a CO2 evolution pressure curve, a 14C age, and stable isotope profiles from at least 5 successive dissolution increments representing nearly total dissolution. The data is used for modeling the interfering effects of the different carbonates on the binder carbonate age. The models help us to interpret the 14C age profiles and identify CO2 increments that are as uncontaminated as possible. The dating method was implemented on medieval and younger mortars from churches in the land Archipelago between Finland and Sweden. The results are used to develop the method for a more general and international use.
    • Performance Evaluation of the New AMS System at Accium BioSciences

      Zoppi, Ugo; Crye, James; Song, Qi; Arjomand, Ali (Department of Geosciences, The University of Arizona, 2007-01-01)
      A new compact accelerator mass spectrometry (AMS) system dedicated to the measurement of radiocarbon has been commissioned at the Accium BioSciences headquarters in Seattle. The entire facility (including ancillary laboratories for the preparation of graphite targets) has been designed to handle samples with a wide range of 14C concentrations. In this paper, we discuss the technical details of the new facility and present performance test results demonstrating state-of-the-art capabilities. In particular, modern samples can be readily measured with 0.3% precision and accuracy, machine background levels are consistently in the low 1016 (14C/12C), and chemical background is approximately equivalent to a fraction of modern of 0.004. In addition, when 100-times-modern samples were processed, no increase in background was observed, either during sample processing or during AMS measurement. This corresponds to a dynamic range for 14C analysis of 6 orders of magnitude.
    • Ultra-Microscale (5-25 μg C) Analysis of Individual Lipids by 14C AMS: Assessment and Correction for Sample Processing Blanks

      Shah, Sunita R.; Pearson, Ann (Department of Geosciences, The University of Arizona, 2007-01-01)
      Measurements of the natural abundance of radiocarbon in biomarker molecules can be used to elucidate the biogeochemical roles of marine bacteria and archaea in the oceanic water column. However, the relatively low concentration of biomass, especially below the euphotic zone, inevitably results in small sample sizes for compound-specific analyses. In ultra-microscale 14C measurements, which we define as measurements on samples smaller than 25g C, the process of isolating pure compounds and preparing them for measurement adds significant background carbon. This additional blank carbon can contribute up to 40% of the total sample mass; therefore, it is necessary to quantify all components of the processing blank in order to make appropriate corrections. Complete propagation of error is critical in order to report the correct analytical uncertainty. The carbon blank is composed of at least 3 different sources: i) those that scale in proportion to the mass of the sample; ii) sources that contribute a constant mass of blank, e.g. closed-tube combustion; and iii) contaminants from vacuum lines and/or other aspects of sample handling that are difficult to quantify. We approached the problem of correcting for the total sample processing blank by deriving a 4-part isotopic mass balance based on separating the 3 exogenous components from the sample. Subsequently, we derived the appropriate equations for the full propagation of error associated with these corrections. Equations for these terms are presented. Full treatment of a set of raw data is demonstrated using compound-specific 14C data from the North Central Pacific water column.
    • Radiocarbon Dates from the Pleistocene Fossil Deposits of Samwel Cave, Shasta County, California, USA

      Feranec, Robert S.; Hadly, Elizabeth A.; Blois, Jessica L.; Barnosky, Anthony D.; Paytan, Adina (Department of Geosciences, The University of Arizona, 2007-01-01)
      Dates obtained from the collagen of 5 mammals from the fossil deposits of Samwel Cave, Shasta County, California, USA, show emplacement during the last glacial maximum. These dates support the assignment of the fauna to the late Pleistocene. The Samwel Cave deposits currently do not appear to be stratified.
    • Background Concentration of 14C in Aquatic Samples from Brackish Lake Obuchi, Rokkasho, Japan, Adjacent to Nuclear Fuel Reprocessing Facilities

      Ueda, Shinji; Kondo, Kunio; Inaba, Jiro (Department of Geosciences, The University of Arizona, 2007-01-01)
      The brackish Lake Obuchi in Rokkasho, Japan, is adjacent to the first Japanese commercial nuclear fuel reprocessing facilities, which are now undergoing performance testing, with commercial operation scheduled to start in 2007. Preparatory surveys were made by measuring the background levels of radiocarbon for water, aquatic biota, and sediment samples using accelerator mass spectrometry (AMS) in order to study the potential effects of 14C released by the plant to the 14C concentration in aquatic samples. Concentrations of 14C in Futamata River in 2004 ranged from 102 +/- 0.5 to 109 +/- 0.6 pMC (average 106 +/- 0.6 pMC), while 14C concentrations in brackish water from Lake Obuchi and in seawater were 89 +/- 0.5 to 104 +/- 0.4 pMC (average 98 +/- 0.5 pMC) and 82 +/- 0.6 to 102 +/- 0.4 pMC (average 93 +/- 0.5 pMC), respectively. The relationship between 14C concentration and salinity showed a negative correlation (r = 0.68, P < 0.01, n = 20). 14C concentration in selected aquatic biota (i.e. fish, benthos, and seagrass) from 2003 to 2004 ranged from 105 0.7 to 107 0.6 pMC and in zooplankton and phytoplankton was 103 +/- 2.4 to 105 +/- 1.7 pMC. The depth profile of 14C in 3 core sediment samples from Lake Obuchi showed maximum concentrations from 103 +/- 0.5 to 106 +/- 0.5 pMC at 520 cm depth. The vertical profile of 14C concentration in the sediment did not follow global atmospheric 14C fallout. We confirmed that the background level of 14C concentration in aquatic samples in brackish Lake Obuchi before operation of the reprocessing plant was similar to the concentration (~106 pMC) in the recent atmosphere.
    • Hiatus in Prehistoric Chronology of the Cis-Baikal Region, Siberia: Pattern or Artifact?

      Kuzmin, Yaroslav Y. (Department of Geosciences, The University of Arizona, 2007-01-01)
      The problem of a hiatus at about 61005300 BP (about 49004200 cal BC) in the prehistoric chronology of the Cis-Baikal region in Siberia is discussed. Based on a critical evaluation of existing evidence, there was no discontinuity found in the cultural sequence between the Kitoi and Serovo/Glazkovo complexes of the Neolithic, and the proposed hiatus may be an artifact based on underestimation of solid data. Conventional 14C dates are presented that were generated in the 1980s to early 2000s for Cis-Baikal prehistoric burial grounds, and were later dated by the accelerator mass spectrometry (AMS).
    • Quantitative Extraction of Dissolved Inorganic Carbon (as CO2) and Water by Vacuum Distillation from Sediments of the Unsaturated Zone for Carbon Isotope Analysis (13C and 14C)

      Carmi, I.; Kronfeld, J.; Yechieli, Y.; Yakir, D.; Stiller, M.; Boaretto, M. (Department of Geosciences, The University of Arizona, 2007-01-01)
      Vacuum distillation is shown to be useful for the quantitative extraction of dissolved inorganic carbon (as CO2) and water from sediments of the unsaturated zone in the Coastal Aquifer of Israel. Several tests of vacuum extractions from tap water and sediments are presented, including standard addition, which show that the distillation procedure is quantitative, with minimal or no carbon isotope fractionation. The optimal temperature of the sediment during the extraction was also defined. Examples of vacuum extractions of sediments are shown.
    • Report on the First Stage of the Iron Age Dating Project in Israel: Supporting a Low Chronology

      Sharon, Ilan; Gilboa, Ayelet; Jull, A. J. Timothy; Boaretto, Elisabetta (Department of Geosciences, The University of Arizona, 2007-01-01)
      The traditional chronology of ancient Israel in the 11th-9th centuries BCE was constructed mainly by correlating archaeological phenomena with biblical narratives and with Bible-derived chronology. The chronology of Cyprus and Greece, and hence of points further west, are in turn based on that of the Levant. Thus, a newly proposed chronology, about 75100 yr lower than the conventional one, bears crucial implications not only for biblical history and historiography but also for cultural processes around the Mediterranean. A comprehensive radiocarbon program was initiated to try and resolve this dilemma. It involves several hundreds of measurements from 21 sites in Israel. Creating the extensive databases necessary for the resolution of tight chronological problems typical of historical periods involves issues of quality control, statistical treatment, modeling, and robustness analysis. The results of the first phase of the dating program favor the new, lower chronology.
    • Radiocarbon Chronologies of Holocene Lacustrine Sediments from the Southern Coast of Buenos Aires Province, Argentina

      Fontana, Sonia L. (Department of Geosciences, The University of Arizona, 2007-01-01)
      Two lacustrine sediment sequences, La Olla 1 and Laguna del Sauce Grande, on the southern coast of Buenos Aires Province, Argentina, were investigated for carbon reservoir effects, which may influence age-depth chronologies. Fruits of the submerged macrophyte Ruppia cf. maritima from the La Olla 1 sequence, and gastropod shells of Heleobia parchappii from the Laguna del Sauce Grande core, were radiocarbon dated. In addition, terrestrial plant remains and shells of living specimens were dated to assess the presence and magnitude of a reservoir effect. A reservoir age of about 800 14C yr is estimated for the aquatic plant samples of La Olla 1 for the early Holocene. The reservoir effect is attributed to the inwash of 14C-deficient bicarbonate from the surrounding sand dunes. The decay of marine organisms and salt spray are likely the main sources of 14C-deficient carbon. The magnitude of the reservoir effect is consistent with marine reservoir offsets reported for the region. The 14C measurements on shells of living and fossil specimens of Heleobia parchappii indicate the absence of a reservoir effect at Laguna del Sauce Grande, which may be due to the large size and shallow nature of the lake. This study shows how the reservoir ages of 2 close-by lakes in very similar geological settings can be largely different. These results have significant implications for the interpretation of 14C dates from lacustrine deposits in the region.
    • Contents

      Department of Geosciences, The University of Arizona, 2007-01-01
    • From the Editor

      Jull, A. J. Timothy (Department of Geosciences, The University of Arizona, 2007-01-01)
    • Disentangling Geomagnetic and Precipitation Signals in an 80-kyr Chinese Loess Record of 10Be

      Zhou, Weijian; Priller, Alfred; Beck, J. Warren; Zhengkun, Wu; Maobai, Chen; Zhisheng, An; Kutschera, Walter; Feng, Xian; Huagui, Yu; Lin, Liu (Department of Geosciences, The University of Arizona, 2007-01-01)
      The cosmogenic radionuclide 10Be is produced by cosmic-ray spallation in Earths atmosphere. Its production rate is regulated by the geomagnetic field intensity, so that its accumulation rate in aeolian sediments can, in principle, be used to derive high-resolution records of geomagnetic field changes. However, 10Be atmospheric fallout rate also varies locally depending on rainfall rate. The accumulation rate of 10Be in sediments is further complicated by overprinting of the geomagnetic and precipitation signals by 10Be attached to remobilized dust, which fell from the atmosphere at some time in the past. Here, we demonstrate that these signals can be deconvoluted to derive both geomagnetic field intensity and paleoprecipitation records of Asian Monsoon intensity in an 80,000-yr-long 10Be record from Chinese loess. The strong similarity between our derived paleomagnetic intensity record and the SINT 200 (Guyodo and Valet 1996) and NAPIS 75 (Laj et al. 2002) stacked marine records suggests that this method might be used to produce multimillion-yr-long records of paleomagnetic intensity from loess. This technique also reveals a new method for extracting quantitative paleoprecipitation records from continental interior regions. Our derived precipitation record is broadly similar to the speleothem delta-18O-based records of paleo-Asian Monsoon intensity from Dongge (Yuan et al. 2004) and Hulu (Wang et al. 2001) caves, and suggests that the paleo-Asian Monsoon intensity may be responding to a combination of both Northern and Southern Hemisphere insolation forcing.
    • Editorial Board

      Department of Geosciences, The University of Arizona, 2007-01-01